// Copyright (c) 2022 NetEase, Inc. All rights reserved.
// Use of this source code is governed by a MIT license that can be
// found in the LICENSE file.

package com.netease.yunxin.kit.entertainment.common.livedata;

import android.util.Log;
import androidx.annotation.MainThread;
import androidx.annotation.Nullable;
import androidx.lifecycle.LifecycleOwner;
import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.Observer;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * A lifecycle-aware observable that sends only new updates after subscription, used for events like
 * navigation and Snackbar messages.
 *
 * <p>This avoids a common problem with events: on configuration change (like rotation) an update
 * can be emitted if the observer is active. This LiveData only calls the observable if there's an
 * explicit call to setValue() or call().
 *
 * <p>Note that only one observer is going to be notified of changes.
 */
public class SingleLiveEvent<T> extends MutableLiveData<T> {

  private static final String TAG = "SingleLiveEvent";

  private final AtomicBoolean mPending = new AtomicBoolean(false);

  @MainThread
  public void observe(LifecycleOwner owner, final Observer<? super T> observer) {

    if (hasActiveObservers()) {
      Log.w(TAG, "Multiple observers registered but only one will be notified of changes.");
    }

    // Observe the internal MutableLiveData
    super.observe(
        owner,
        new Observer<T>() {
          @Override
          public void onChanged(@Nullable T t) {
            if (mPending.compareAndSet(true, false)) {
              observer.onChanged(t);
            }
          }
        });
  }

  @MainThread
  public void setValue(@Nullable T t) {
    mPending.set(true);
    super.setValue(t);
  }

  /** Used for cases where T is Void, to make calls cleaner. */
  @MainThread
  public void call() {
    setValue(null);
  }
}
